Phenol and substituted phenols are important products in the chemical industry and are useful in, for example, the production of phenolic resins, bisphenol A, ε-caprolactam, adipic acid, and plasticizers.
Currently, the most common route for the production of phenol is the Hock process. This is a three-step process in which the first step involves alkylation of benzene with propylene to produce cumene, followed by oxidation of the cumene to the corresponding hydroperoxide and then cleavage of the hydroperoxide to produce equimolar amounts of phenol and acetone. However, the world demand for phenol is growing more rapidly than that for acetone. In addition, the cost of propylene relative to that of butenes is likely to increase, due to a developing shortage of propylene.
Thus, a process that uses butenes or higher alkenes instead of propylene as feed and coproduces methyl ethyl ketone (MEK) or higher ketones, such as cyclohexanone, rather than acetone may be an attractive alternative route to the production of phenols. For example, there is a growing market for MEK, which is useful as a lacquer, a solvent and for dewaxing of lubricating oils. In addition, cyclohexanone is used as an industrial solvent, as an activator in oxidation reactions and in the production of adipic acid, cyclohexanone resins, cyclohexanone oxime, caprolactam and nylon 6.
It is known that phenol and MEK can be produced from sec-butylbenzene, in a process where sec-butylbenzene is oxidized to obtain sec-butylbenzene hydroperoxide and the peroxide decomposed to the desired phenol and methyl ethyl ketone. An overview of such a process is described in pages 113-121 and 261-263 of Process Economics Report No. 22B entitled “Phenol”, published by the Stanford Research Institute in December 1977.
However, in comparison to cumene, oxidation of aromatic compounds substituted by branched alkyl groups having 4 or more carbon atoms, such as sec-butylbenzene, to the corresponding hydroperoxide requires higher temperatures and is very sensitive to the presence of impurities. For example, in the case of sec-butylbenzene containing 1% by weight of isobutylbenzene, the rate of formation of sec-butylbenzene hydroperoxide decreases to about 91% of that when the sec-butylbenzene is free of isobutylbenzene. Similarly, when the isobutylbenzene content is 1.65% by weight, the rate of oxidation decreases to about 86%; when the isobutylbenzene content is 2% by weight, the rate of oxidation decreases to about 84%; and when the isobutylbenzene content is 3.5% by weight, the rate of oxidation decreases to as low as about 82%.
Thus there remains a need to find an oxidation process for producing C4+ alkyl aromatic hydroperoxides, and particularly sec-butylbenzene hydroperoxide, that is much less sensitive to the presence of impurities than the existing oxidation processes, and that allows efficient commercial scale production of phenol and MEK or higher ketones.
U.S. Pat. No. 5,298,667 (Sumitomo) and EP-A-548,986 (Sumitomo) disclose a process for producing phenol and MEK which comprises the steps of (I) oxidizing a material selected from (A) sec-butylbenzene substantially free from ethyl hydroperoxide, carboxylic acids and phenol, (B) sec-butylbenzene substantially free from styrenes, and (C) sec-butylbenzene substantially free from methylbenzyl alcohol, to obtain sec-butylbenzene hydroperoxide, with an oxygen-containing gas and in the absence of a catalyst, and (II) decomposing the sec-butylbenzene hydroperoxide to obtain phenol and MEK with an acidic catalyst.
EP-A-1,088,809 (Phenolchemie) discloses a process for producing phenol, MEK and acetone by the oxidation of a mixture containing cumene and up to 25 wt % sec-butylbenzene and the subsequent Hock cleavage of the hydroperoxides, so that the ratio of the phenol:acetone:MEK in the product can be controlled via the composition of the feed mixture. The feed mixture is produced directly by the alkylation of benzene with a corresponding mixture of propene and 1-butene/2-butene in the presence of a commercial alkylation catalyst such as AlCl3, H3PO4/SiO2 or a zeolite. Oxidation takes place in the presence of air or oxygen and in the absence of a catalyst.
FR-A-2,182,802 (Union Carbide) discloses a process for producing phenol and MEK by oxidation of sec-butylbenzene, in which sec-butylbenzene is oxidized to sec-butylbenzene hydroperoxide in the presence of air and optionally in the presence of sec-butylbenzene hydroperoxide, followed by peroxide decomposition. According to this document, the sec-butylbenzene must not contain more than 1 wt % isobutylbenzene, since the presence of isobutylbenzene significantly reduces the overall process efficiency and hence the yield of phenol and MEK.
Japanese Patent Application Publication No. 62/114922, published May 26, 1987, discloses that sec-butylbenzene can be oxidized with a gas containing molecular oxygen, preferably air, in the presence of cumene or cumene hydroperoxide at a temperature of 90 to 145° C. and a pressure of 1 to 20 kg/cm2G.
U.S. Patent Application Publications Nos. 2004/0162448 (Shell) and 2004/0236152 (Shell) disclose processes for producing phenol and acetone and/or MEK, in which a mixture of cumene and sec-butylbenzene is oxidized to the corresponding peroxides in the presence of oxygen, followed by peroxide decomposition. In the Examples, the oxidation mixture also contains 1% cumene hydroperoxide as an initiator. According to these documents, the addition of a neutralizing base in the oxidation mixture improves the yield in hydroperoxide and reduces the formation of undesired side products.
U.S. Pat. No. 6,852,893 (Creavis) and U.S. Pat. No. 6,720,462 (Creavis) describe methods for producing phenol by catalytic oxidation of alkyl aromatic hydrocarbons to the corresponding hydroperoxide, and subsequent cleavage of the hydroperoxide to give phenol and a ketone. Catalytic oxidation takes place with oxygen, in the presence of a free radical initiator and a catalyst, typically an N-hydroxycarbodiimide catalyst, such as N-hydroxyphthalimide. Preferred substrates that may be oxidized by this process include cumene, cyclohexylbenzene, cyclododecylbenzene and sec-butylbenzene.
U.S. Pat. No. 4,136,123 (Goodyear) discloses a process for oxidizing alkylaromatic compounds to the corresponding hydroperoxides in the presence of a sulfonated metallo phthalocyanine catalyst and a free radical initiator selected from the group consisting of alkyl hydroperoxides having from 4 to 6 carbon atoms and aralkyl hydroperoxides having from 8 to 14 carbon atoms.
U.S. Pat. No. 4,282,383 (Upjohn) describes a process for making cyclohexylbenzene hydroperoxide useful as an intermediate in the formation of phenol and cyclohexanone. The process involves heating cyclohexylbenzene at a temperature in the range of about 80° C. to about 105° C. in the presence of oxygen and from about 2 to 6 percent by weight, based on cyclohexylbenzene, of a hydroperoxide selected from the group consisting of tertiary-butyl hydroperoxide, cumene hydroperoxide and p-diisopropylbenzene dihydroperoxide, and from about 0.1 to 5 percent by weight, based on cyclohexylbenzene, of a free radical initiator selected from the group consisting of azabisisobutyronitrile, t-butylperbenzoate and dicumyl peroxide.
U.S. Pat. No. 4,450,303 (Phillips Petroleum) describes a process for making secondary alkyl substituted benzene hydroperoxides by heating a secondary alkyl substituted benzene, such as cyclohexylbenzene, cumene, sec-butylbenzene, sec-pentylbenzene, p-methyl-sec-butylbenzene, 1,4-diphenylcyclohexane, para-dicyclohexylbenzene, and sec-hexylbenzene, at a temperature of about 60° C. to 200° C. in the presence of oxygen. The heating is also conducted in the presence of from about 0.05 to 5 wt % of a samarium catalyst of the formula R″COOSm wherein R″ is a C1 to C20 alkyl, aryl, alkaryl, or aralkyl radical and optionally a free radical initiator selected from the group consisting of azo-type compounds and peroxide compounds. In one embodiment, the secondary alkyl substituted benzene is cyclohexylbenzene, the catalyst is samarium acetate and the free radical initiator is cumene hydroperoxide.
The article by Sheldlon et al entitled “Organocatalytic Oxidations Mediated by Nitroxyl Radicals” in Adv. Synth. Catal., 2004, 346, pages 1051-1071 discloses that cyclohexylbenzene (CHB) can be oxidized to the 1-hydroperoxide with 97.6% selectivity at 32% CHB conversion at 100° C. in the presence of 0.5 mol % of a N-hydroxyphthalimide catalyst and 2 mol % of the product hydroperoxide as a free radical initiator.
U.S. Pat. No. 3,959,381 (Texaco) discloses a method of preparing phenol and cyclohexanone by contacting a mixture of cyclohexylbenzene and cumene or cumene hydroperoxide at a mole ratio of 1:99 and 99:1 with an oxygen containing gas at a temperature between about 90 and 140° C. and a mole ratio of oxygen to cyclohexylbenzene of at least 3:1 to form a second mixture of 1-phenylcyclohexyl hydroperoxide and cumyl hydroperoxide, and subsequently removing excess cumene and at least a portion of excess cyclohexylbenzene from the second mixture followed by contacting the second mixture with an alkanone of from 3 to 6 carbons and an acid cleavage catalyst selected from hydrocarbyl sulfonic acid and mineral acid at a temperature between about 20 and 50° C. and recovering phenol and cyclohexanone from the final product.
According to the invention, it has now been found that certain secondary alkyl substituted benzenes, including sec-butylbenzene and cyclohexylbenzene, can be oxidized to the corresponding hydroperoxide in the presence of tert-butyl hydroperoxide, but in the absence of other catalysts.